Sheet containing two-dimensional hydrogen boride and production method for sheet containing two-dimensional boron compound

ABSTRACT

A two-dimensional hydrogen boride-containing sheet of the present invention has a two-dimensional network that consists of (HB)n (n≥4).

TECHNICAL FIELD

The present invention relates to a two-dimensional hydrogenboride-containing sheet and a production method for a two-dimensionalboron compound-containing sheet.

BACKGROUND ART

In recent years, a phenomenon with novel functionalities involved hasbeen found for substances in which atoms form a two-dimensional network(hereinafter referred to as “atomic network substances”). In addition,the atomic network substances have attracted attention for theirpotential as functional materials. Although not sufficiently developed,the potential of the atomic network substances may be consideredsuperior to other materials. As the potential of the atomic networksubstances which is superior to other materials, for example, creationand control of functions by insertion of metal atoms into the atomicnetworks, selection thereof, or the like, flexibility of the atomicnetworks, a function as catalyst carriers or catalysts utilizing a widespecific surface area, high functionality inherent in the atomicnetworks, and the like are mentioned.

In addition, the atomic network substances form a matrix of a metal, asemiconductor, or an insulator by a network structure. Insertion ofmetal atoms into the atomic networks causes charge transfer, which makesit possible to control electronic properties. Graphene in which onlycarbon atoms form a two-dimensional network has better electricalconductivity than silicon and better strength than iron. In addition,graphene is expected to be applied in various fields includingsemiconductor materials and electrode materials for secondary batteries.In addition, a two-dimensional boron sheet in which boron atoms form atwo-dimensional network is also expected to have similar properties tographene.

As a method of synthesizing a two-dimensional boron sheet, for example,a method of decomposing diborane at high temperature is known (see, forexample, Non Patent Literature 1).

CITATION LIST Non Patent Literature

[Non Patent Literature 1]

-   Ultrathin Nanosheets: Ultrathin Single-Crystalline Boron Nanosheets    for Enhanced Electro-Optical Performances, Junqi Xu, Yangyang Chang,    Lin Gan, Ying Ma and Tianyou Zhai Advanced Science, 2 (2015)    1500023.

SUMMARY OF INVENTION Technical Problem

However, in the related art, a production method for a two-dimensionalboron compound-containing sheet, which consists of boron atoms and otheratoms, and has high functionality, has not been established. Therefore,it was not possible to produce a two-dimensional boroncompound-containing sheet.

The present invention has been made in view of the above circumstances,and an object thereof is to provide a two-dimensional hydrogenboride-containing sheet which has a two-dimensional network thatconsists of boron atoms and other atoms such as hydrogen, and aproduction method for a two-dimensional boron compound-containing sheet.

Solution to Problem

[1] A two-dimensional hydrogen boride-containing sheet, including:

a two-dimensional network that consists of (HB)_(n) (n≥4).

[2] The two-dimensional hydrogen boride-containing sheet according to[1],

in which in the two-dimensional network, boron atoms are arranged in ahexagonal ring shape, hexagons formed of the boron atoms are connectedto one another to form a mesh-like shape, and the two-dimensionalnetwork has a site at which two adjacent boron atoms amongst the boronatoms are bound to the same hydrogen atom.

[3] The two-dimensional hydrogen boride-containing sheet according to[1] or [2],

in which a length in at least one direction is 100 nm or longer.

[4] A production method for a two-dimensional boron compound-containingsheet, including:

a step of mixing, in a polar organic solvent, metal diboride having anMB₂-type (where M is at least one selected from the group consisting ofAl, Mg, Ta, Zr, Re, Cr, Ti, and V) structure with an ion exchange resinin which ions exchangeable with metal ions constituting the metaldiboride are coordinated.

[5] The production method for a two-dimensional boroncompound-containing sheet according to [4],

in which the ion exchange resin has a sulfo group.

[6] The production method for a two-dimensional boroncompound-containing sheet according to [4] or [5],

in which the polar organic solvent is acetonitrile or methanol.

Advantageous Effects of Invention

According to the present invention, it is possible to provide atwo-dimensional hydrogen boride-containing sheet which has atwo-dimensional network that consists of boron atoms and other atomssuch as hydrogen, and can be used as an electronic material, a catalystcarrier material, a catalyst material, a superconducting material, orthe like, and a production method for a two-dimensional boroncompound-containing sheet.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1A is a schematic diagram representing an XY plane of a molecularstructure of a two-dimensional hydrogen boride-containing sheet of thepresent invention.

FIG. 1B is a schematic diagram representing a YZ plane of the molecularstructure of the two-dimensional hydrogen boride-containing sheet of thepresent invention.

FIG. 1C is a schematic diagram representing a ZX plane of the molecularstructure of the two-dimensional hydrogen boride-containing sheet of thepresent invention.

FIG. 2 is a graph representing the results of X-ray photoelectronspectroscopy in Experimental Example 1.

FIG. 3 is a graph representing the results of X-ray photoelectronspectroscopy in Experimental Example 2.

FIG. 4 is a scanning-type transmission electron microscopic image inExperimental Example 3.

FIG. 5 is a scanning-type transmission electron microscopic image inExperimental Example 3.

FIG. 6 is a scanning-type transmission electron microscopic image inExperimental Example 3.

FIG. 7 is a scanning-type transmission electron microscopic image inExperimental Example 3.

FIG. 8 is a scanning-type transmission electron microscopic image inExperimental Example 3.

FIG. 9 is a scanning-type transmission electron microscopic image inExperimental Example 4;

FIG. 10 is a scanning-type transmission electron microscopic image ofExperimental Example 4.

FIG. 11 is a scanning-type transmission electron microscopic image ofExperimental Example 4.

FIG. 12 is a scanning-type transmission electron microscopic image inExperimental Example 4.

FIG. 13 is a scanning-type transmission electron microscopic image ofExperimental Example 5.

FIG. 14 is a graph representing the results of electron energy lossspectroscopy in Experimental Example 5.

FIG. 15 is a graph representing the results of electron energy lossspectroscopy in Experimental Example 5.

FIG. 16 is a graph representing the results of thermal desorptionspectroscopy in Experimental Example 6.

FIG. 17 is a graph representing the results of visible ultravioletspectroscopy in Experimental Example 7.

FIG. 18 is a scanning-type transmission electron microscopic image inExperimental Example 8.

FIG. 19 is a graph representing the results obtained by measuring athickness of a portion indicated by L in a scanning-type transmissionelectron microscopic image in Experimental Example 8.

FIG. 20 is a graph representing the results of Fourier transforminfrared spectroscopy in Experimental Example 9.

DESCRIPTION OF EMBODIMENTS

Embodiments of the two-dimensional hydrogen boride-containing sheet andthe production method for a two-dimensional boron compound-containingsheet of the present invention will be described.

The present embodiments are specifically described for betterunderstanding of the spirit of the invention, and are not intended tolimit the present invention unless otherwise specified.

[Two-Dimensional Hydrogen Boride-Containing Sheet]

The two-dimensional hydrogen boride-containing sheet of the presentembodiment is a sheet having a two-dimensional network that consists of(HB)_(n) (n≥4, where n is an integer). That is, in the two-dimensionalhydrogen boride-containing sheet of the present embodiment, boron atoms(B) and hydrogen atoms (H) are present at a molar ratio of 1:1. Inaddition, the two-dimensional hydrogen boride-containing sheet of thepresent embodiment is a sheet having a two-dimensional network formed ofonly boron atoms (B) and hydrogen atoms (H).

In addition, in (HB)_(n) (n≥4, where n is an integer), a case where n=4represents a unit cell of the two-dimensional hydrogen boride-containingsheet of the present embodiment.

In the two-dimensional hydrogen boride-containing sheet of the presentembodiment, boron atoms (B) are arranged in a hexagonal ring shape likea benzene ring, as shown in FIG. 1A. In addition, boron atoms (B) arepresent at the apexes of the hexagon. Furthermore, the hexagons formedof the boron atoms (B) are connected to one another without gaps to forma mesh-like surface structure (two-dimensional network). As shown inFIGS. 1B and 1C, the two-dimensional hydrogen boride-containing sheet ofthe present embodiment has a site at which two adjacent boron atoms (B)amongst the boron atoms are bound to the same hydrogen atom (H).

In the two-dimensional hydrogen boride-containing sheet of the presentembodiment, a hexagonal mesh-like shape formed of the boron atoms (B)refers, for example, to a honeycomb shape.

Such a two-dimensional hydrogen boride-containing sheet of the presentembodiment is a thin film-like substance having a two-dimensionalnetwork that consists of boron atoms (B) and hydrogen atoms (H). Inaddition, the two-dimensional hydrogen boride-containing sheet of thepresent embodiment contains almost no either metal atoms derived frommetal diboride used in the production method for a two-dimensional boroncompound-containing sheet of the present embodiment as will be describedlater, or other metal atoms.

In the two-dimensional hydrogen boride-containing sheet of the presentembodiment, the total number of boron atoms (B) and hydrogen atoms (H)forming the above-mentioned mesh-like surface structure is 1,000 ormore.

A bonding distance d₁ between two adjacent boron atoms (B) as shown inFIG. 1A is 0.17 nm to 0.18 nm. In addition, a bonding distance d₂between two adjacent boron atoms (B) via one hydrogen atom (H) as shownin FIG. 1B is 0.17 nm to 0.18 nm. In addition, a bonding distance d₃between adjacent boron atom (B) and hydrogen atom (H) as shown in FIG.1B is 0.125 nm to 0.135 nm.

A thickness of the two-dimensional hydrogen boride-containing sheet ofthe present embodiment is 0.23 nm to 0.50 nm.

In the two-dimensional hydrogen boride-containing sheet of the presentembodiment, a length in at least one direction (for example, a length inthe X direction or Y direction in FIG. 1A) is preferably 100 nm orlonger. In the two-dimensional hydrogen boride-containing sheet of thepresent embodiment, in a case where the length in at least one directionis 100 nm or longer, the two-dimensional hydrogen boride-containingsheet of the present embodiment can be effectively used as an electronicmaterial, a catalyst carrier material, a catalyst material, asuperconducting material, or the like.

A size (area) of the two-dimensional hydrogen boride-containing sheet ofthe present embodiment is not particularly limited. The two-dimensionalhydrogen boride-containing sheet of the present embodiment can be formedin any size by the production method for a two-dimensional boroncompound-containing sheet of the present embodiment as described later.

Such a two-dimensional hydrogen boride-containing sheet of the presentembodiment is a substance having a crystal structure. In addition, inthe two-dimensional hydrogen boride-containing sheet of the presentembodiment, a strong bonding strength is exhibited between the boronatoms (B) forming the hexagonal ring and between the boron atom (B) andthe hydrogen atom (H). Therefore, even if a plurality of the sheetscontaining two-dimensional hydrogen boride of the present embodiment arestacked to form a crystal (aggregate) at the time of production, thecrystal can be easily cleaved along a crystal plane similarly tographite and separated (recovered) as single-layer two-dimensionalsheets.

The two-dimensional hydrogen boride-containing sheet of the presentembodiment can be used as an electronic material, a catalyst carriermaterial, a superconducting material, or the like.

It is predicted that the two-dimensional hydrogen boride-containingsheet of the present embodiment exhibits an electronic structure calledDirac Fermion that exhibits the same mobility as graphene (seeTwo-Dimensional Boron Hydride Sheets: High Stability, Massless DiracFermions, and Excellent Mechanical Properties, Angew. Chem. Int. Ed.,2016, 55, 1.). Therefore, the two-dimensional hydrogen boride-containingsheet of the present embodiment is expected to be used as a newelectronic device material.

In addition, a two-dimensional sheet of boron is predicted to be asuperconductor at 10 K to 20 K (see Can Two-Dimensional BoronSuperconduct?, Evgeni S. Penev, Alex Kutana, and Boris I. Yakobson, NanoLett., 2016, 16, 2522). Therefore, the two-dimensional hydrogenboride-containing sheet of the present embodiment is expected to be usedas a new matrix material for superconductors which exceeds thetwo-dimensional sheet of boron.

In addition, the two-dimensional sheet of boron is predicted to havefour times mechanical strength of iron (see Mechanical properties andStabilities of α-boron monolayers, Peng Q, Han L, Wen X, Liu S, Chen Z,Lian J, De S., Phys. Chem. Chem. Phys. 2015, 17, 2160). Therefore, thetwo-dimensional hydrogen boride-containing sheet of the presentembodiment is expected to be used as a new matrix material forhigh-strength materials which exceeds the two-dimensional sheet ofboron.

In addition, it is predicted that the surface of the two-dimensionalsheet of boron can be coated with lithium to provide hydrogen storagecharacteristics of 12.3 mass % (Boron-double-ring sheet, fullerene, andnanotubes: potential hydrogen storage materials, Wang J, Zhao H Y, LiuY., Chem. Phys. Chem. 2014, 15, 3453). Therefore, the two-dimensionalhydrogen boride-containing sheet of the present embodiment is expectedto be used as a new hydrogen storage material which exceeds thetwo-dimensional sheet of boron.

In addition, in a case where the two-dimensional sheet of boron is usedfor an electrode of a lithium ion secondary battery, it is predictedthat the lithium ion secondary battery, provided with the electrode forwhich the two-dimensional sheet of boron is used, has four times thecapacity of a lithium ion secondary battery provided with an electrodeconsisting of graphite (Borophene: A promising anode material offeringhigh specific capacity and high rate capability for lithium-ionbatteries, H. R. Jiang, Ziheng Lu, M. C. Wu, Francesco Ciucci, T. S.Zhao, Nano Energy 23 (2016) 97). Therefore, the two-dimensional hydrogenboride-containing sheet of the present embodiment is expected to be usedas a new electrode material for lithium ion secondary batteries whichexceeds the two-dimensional sheet of boron.

Furthermore, from the viewpoint that the two-dimensional sheet of boronreleases hydrogen when heated (hydrogen comes out during burning thereofand explosion occurs due to hydrogen), the two-dimensional hydrogenboride-containing sheet of the present embodiment is expected to be usedas a solid fuel.

[Production Method for Sheet Containing Two-Dimensional Boron Compound]

The production method for a two-dimensional boron compound-containingsheet of the present embodiment is a method, including a step of mixing(hereinafter referred to as “first step”), in a polar organic solvent,metal diboride having an MB₂-type structure (where M is at least oneselected from the group consisting of Al, Mg, Ta, Zr, Re, Cr, Ti, and V)with an ion exchange resin in which ions exchangeable with metal ionsconstituting the metal diboride are coordinated.

As the metal diboride having an MB₂-type structure, metal diboridehaving a hexagonal ring structure is used. For example, aluminumdiboride (AlB₂), magnesium diboride (MgB₂), tantalum diboride (TaB₂),zirconium diboride (ZrB₂), rhenium diboride (ReB₂), chromium diboride(CrB₂), titanium diboride (TiB₂), and vanadium diboride (VB₂) are used.

It is preferable to use magnesium diboride, from the viewpoint that ionexchange with an ion exchange resin can be easily performed in a polarorganic solvent.

There is no particular limitation on the ion exchange resin in whichions exchangeable with metal ions constituting the metal diboride arecoordinated. As such an ion exchange resin, for example, a polymer ofstyrene having a functional group in which ions exchangeable with metalions constituting the metal diboride are coordinated (hereinafterreferred to as “functional group α”), a polymer of divinylbenzene havingthe functional group α, a copolymer of styrene having the functionalgroup α and divinylbenzene having the functional group α, and the likeare mentioned.

As the functional group α, for example, a sulfo group, a carboxyl group,and the like are mentioned. Among these, a sulfo group is preferable,from the viewpoint that ion exchange with metal ions constituting themetal diboride can be easily performed in a polar organic solvent.

The polar organic solvent is not particularly limited. For example,acetonitrile, N,N-dimethylformamide, methanol, and the like arementioned. Among these, acetonitrile is preferable from the viewpointthat no oxygen is contained.

In the first step, the metal diboride and the ion exchange resin areintroduced into the polar organic solvent, and a mixed solutioncontaining the polar organic solvent, the metal diboride, and the ionexchange resin is stirred, so that sufficient contact is made betweenthe metal diboride and the ion exchange resin. As a result, ion exchangeoccurs between metal ions constituting the metal diboride and ions ofthe functional group α of the ion exchange resin, so that atwo-dimensional boron compound-containing sheet is produced which has atwo-dimensional network formed of boron atoms and atoms derived from thefunctional group α of the ion exchange resin.

For example, in a case where magnesium diboride is used as the metaldiboride and an ion exchange resin having a sulfo group is used as theion exchange resin, magnesium ion (Mg⁺) of the magnesium diboride isreplaced with hydrogen ion (H⁺) of the sulfo group of the ion exchangeresin, so that a two-dimensional hydrogen boride-containing sheet whichhas the two-dimensional network that consists of boron atoms (B) andhydrogen atoms (H) as described above is produced.

In the first step, it is preferable that an ion-exchange reactionbetween metal ions constituting the metal diboride and ions of thefunctional group α of the ion exchange resin be caused to proceed gentlywithout applying ultrasonic waves or the like to the mixed solution.

In a case where the mixed solution is stirred, a temperature of themixed solution is preferably 15° C. to 35° C.

A time for which the mixed solution is stirred is not particularlylimited, and is, for example, 700 minutes to 7,000 minutes.

In addition, the first step is performed under an inert atmosphereconsisting of an inert gas such as nitrogen (N₂) and argon (Ar).

Next, the mixed solution for which stirring has been completed isfiltered (second step).

A filtration method of the mixed solution is not particularly limited,and, for example, methods such as natural filtration, vacuum filtration,pressure filtration, and centrifugal filtration are used. In addition,as a filter medium, for example, filter paper using cellulose as a basematerial, a membrane filter, a filter plate obtained by compressionmolding of cellulose, glass fiber, or the like, or the like is used.

A solution containing a product recovered by being separated from aprecipitate through filtration is either naturally dried or dried byheating, to finally obtain only the product.

This product is a two-dimensional boron compound-containing sheet whichhas a two-dimensional network formed of boron atoms and atoms derivedfrom the functional group α of the ion exchange resin.

As a method of analyzing the product obtained by the production methodfor a two-dimensional boron compound-containing sheet of the presentembodiment, for example, observation by X-ray photoelectron spectroscopy(XPS), observation by a transmission electron microscope (TEM),observations by energy dispersive X-ray spectroscopy (EDS) and electronenergy loss spectroscopy (EELS) performed in a transmission electronmicroscope, and the like are mentioned.

In X-ray photoelectron spectroscopy (XPS), for example, the surface of aproduct is irradiated with X-rays using an X-ray photoelectronspectrometer (trade name: JPS9010TR) manufactured by JEOL Ltd., andenergy of photoelectrons generated at the time of irradiation ismeasured, thereby analyzing constituent elements of the product andelectronic states thereof. In this analysis, in a case where energy ofphotoelectrons attributable to a metal element constituting the metaldiboride which is a raw material is hardly detected, and only energy ofphotoelectrons attributable to boron and an element derived from thefunctional group α of the ion exchange resin is detected, it can be saidthat the product is composed only of boron and the element derived fromthe functional group α of the ion exchange resin.

In a case of the observation by a transmission electron microscope(TEM), for example, a shape (appearance) and the like of a product areanalyzed by observing the product using a transmission electronmicroscope (trade name: JEM-2100F TEM/STEM) manufactured by JEOL Ltd. Inthis analysis, in a case where a film-like (sheet-like) substance isobserved, it can be said that the product is a two-dimensionalsheet-like substance. By performing energy dispersive X-ray spectroscopy(EDS) in a transmission electron microscope, it is possible to observethe presence or absence of a metal element at a TEM-observed site of theproduct. In this analysis, in a case where X-ray energy attributable toa metal element constituting the metal diboride which is a raw materialis hardly detected, and a peak of the metal element (for example, Mg)does not appear, it can be said that the metal element does not exist.In addition, by performing electron energy loss spectroscopy (EELS) in atransmission electron microscope, constituent elements at a TEM-observedsite of the product can be observed. In this analysis, in a case whereonly X-ray energy attributable to boron and an element derived from thefunctional group α of the ion exchange resin is detected, it can be saidthat the product is composed only of boron and the element derived fromthe functional group α of the above-mentioned ion exchange resin asdescribed above.

According to the production method for a two-dimensional boroncompound-containing sheet of the present embodiment, a two-dimensionalboron compound-containing sheet which has a two-dimensional networkformed of boron atoms and atoms derived from the functional group α ofthe ion exchange resin can be easily produced.

A two-dimensional boron compound-containing sheet having a larger areacan be produced by using a large crystal of metal diboride having aMB₂-type structure which is a raw material.

In addition, according to the production method for a two-dimensionalboron compound-containing sheet of the present embodiment, in order toperform ion-exchange between metal ions constituting the metal diborideand ions of the functional group α of the ion exchange resin, a polarorganic solvent is used instead of using an acidic solution. Therefore,it is not necessary to adjust a pH of the mixed solution containing thepolar organic solvent, the metal diboride, and the ion exchange resin.

In addition, according to the production method for a two-dimensionalboron compound-containing sheet of the present embodiment, in the firststep, for example, in a case where magnesium diboride is used as themetal diboride, and an ion exchange resin having a sulfo group is usedas the ion exchange resin, magnesium ion (Mg⁺) of the magnesium diborideis replaced with hydrogen ion (H⁺) of the sulfo group of the ionexchange resin, so that a minimum unit (HB)₄ can be produced as thetwo-dimensional hydrogen boride-containing sheet.

EXAMPLES

Hereinafter, the present invention will be described more specificallywith reference to experimental examples. However, the present inventionis not limited to the following experimental examples.

Experimental Example 1

X-ray photoelectron spectroscopy (XPS) of magnesium diboride(manufactured by Rare Metallic Co., Ltd.) was performed.

As an analyzer for the X-ray photoelectron spectroscopy, an X-rayphotoelectron spectrometer (trade name: JPS9010TR) manufactured by JEOLLtd. was used. The results of the X-ray photoelectron spectroscopy areshown in FIG. 2.

Experimental Example 2

30 mL by volume of ion exchange resin having a sulfo group (Amberlite(registered trademark) IR120B, manufactured by Organo Corporation) wasadded to acetonitrile while adding 60 mg of magnesium diboride (purity:99%, manufactured by Rare Metallic Co., Ltd.). The resultant was stirredwith a glass rod to prepare a mixed solution of the magnesium diborideand the ion exchange resin.

After the mixed solution was stirred at 25° C. for 72 hours, the mixedsolution was filtered through a membrane filter with a pore size of 1.0μm, and the filtrate was recovered. Thereafter, the filtrate was driedat 80° C. using a hot plate in a nitrogen atmosphere to obtain aproduct.

For the obtained product, X-ray photoelectron spectroscopy was performedin the same manner as in Experimental Example 1. The results are shownin FIG. 3.

In the results in FIG. 2, a peak of Mg2p of magnesium appears at 51.3eV, a peak of B1s of boron appears at 188.2 eV, and a peak of boronoxide (B₂O₃) covering the surface of magnesium diboride (MgB₂) appearsat 193.2 eV. This is consistent with the X-ray photoelectronspectroscopy results for typical commercial MgB₂.

From the results in FIG. 3, the peak of Mg2p which appears in FIG. 2 wasnot observed. As a result, it was found that the product in ExperimentalExample 2 contains no magnesium (Mg) and contains boron (B). In FIG. 3,the small peak appearing at 193.2 eV in FIG. 3 is a peak of boric acidwhich is a by-product. This result suggests that ion exchange hasoccurred between Mg ion of magnesium diboride (MgB₂) and hydrogen ion ofthe sulfo group of the ion exchange resin.

Experimental Example 3

For the product obtained in Experimental Example 2, an observation wasperformed with a scanning-type transmission electron microscope (tradename: JEM-2100F TEM/STEM) manufactured by JEOL Ltd. The observationresults are shown in FIGS. 4 to 8.

From the results in FIGS. 4 to 8, it is considered that the obtainedproduct forms two-dimensional sheets, and respective sheets are in astate in which they are peelable one by one.

Experimental Example 4

For the product obtained in Experimental Example 2 which had beensubjected to heating at 200° C. for 60 minutes, an observation wasperformed with a scanning-type transmission electron microscope (tradename: JEM-2100F TEM/STEM) manufactured by JEOL Ltd. The observationresults are shown in FIGS. 9 to 12.

From the results in FIGS. 9 to 12, it is considered that the obtainedproduct forms two-dimensional sheets, and respective sheets are presentin a state of being peelable one by one.

The product was subjected to heating at 200° C. for dehydration; and theproduct of Experimental Example 4 after being heated to 200° C. and theproduct of Experimental Example 3 are equal in terms of molecularstructure.

Experimental Example 5

For the product obtained in Experimental Example 2, an observation wasperformed with a scanning-type transmission electron microscope (STEM)(trade name: JEM-2100F TEM/STEM) manufactured by JEOL Ltd., and electronenergy loss spectroscopy was performed. The observation results areshown in FIG. 13. In addition, the results of the electron energy lossspectroscopy regarding this product are shown in FIGS. 14 and 15. Asheet-like substance was observed from the results in FIG. 13. Inaddition, as shown in FIG. 14, a peak at 191 eV in the electron energyloss spectroscopy which represents the sp² structure of boron (B) wasobserved, and peaks attributable to carbon (C), nitrogen (N), and oxygen(O) were not observed. From this viewpoint, it was found that thesheet-like substance is composed only of boron having the sp2 structure.In addition, from the results in FIG. 15, no peak attributable tomagnesium (Mg) was observed. From this viewpoint, it was found that thesheet-like substance is composed only of boron. In FIG. 15, peaksattributable to oxygen (O), sulfur (S), copper (Cu), and the like areobserved. However, this represents noise due to high-sensitivitymeasurement.

Experimental Example 6

For the product obtained in Experimental Example 2, thermal desorptionspectroscopy (TDS) was performed with TDS1400TV manufactured by ESCO.The analysis results are shown in FIG. 16. In FIG. 16, (a) represents aspectrum attributable to water, and (b) represents a spectrumattributable to hydrogen. In a case where the product obtained inExperimental Example 2 is heated, it was found that water is eliminatedat around 180° C. due to the presence of boron which is a by-product. Inaddition, in a case where the product obtained in Experimental Example 2is further heated, it was found that hydrogen is eliminated at 200° C.or higher. An amount of water eliminated and an amount of hydrogeneliminated were measured, and a comparison was made for those amounts.As a result, a molar ratio of boron to hydrogen contained in theprecipitate obtained in Experimental Example 2 was calculated to be0.97:1. This result suggests that, in the precipitate obtained inExperimental Example 2, boron atom (B) and hydrogen atom (H) are presentat a molar ratio of 1:1.

Experimental Example 7

For the product obtained in Experimental Example 2, visible ultravioletspectroscopy (UV-VIS) was performed with V-660 manufactured by JASCOCorporation. The analysis results are shown in FIG. 17. From the resultsin FIG. 17, it was found that the product obtained in ExperimentalExample 2 has light absorption at 2.90 eV which is not present inmagnesium diboride or boric acid.

Experimental Example 8

For the product obtained in Experimental Example 2, an observation wasperformed with a scanning-type transmission electron microscope (tradename: JEM-2100F TEM/STEM) manufactured by JEOL Ltd. The observationresults are shown in FIG. 18.

In FIG. 18, a thickness of a portion indicated by L was measured byimage analysis. The analysis results are shown in FIG. 19. From theresults in FIG. 19, it was found that the product obtained inExperimental Example 2 is a sheet-like substance having a thickness ofone to several atomic layers.

Experimental Example 9

For the product obtained in Experimental Example 2, Fourier transforminfrared spectroscopy (FTIR) was performed with FT/IR-300 manufacturedby JASCO Analytical Instruments. The analysis results are shown in FIG.20. From the results in FIG. 20, absorption at 1619 cm⁻¹ was almostidentical to absorption at 1613 cm⁻¹ attributable to the theoreticallycalculated B—H—B bond. In addition, absorption at 2509 cm⁻¹ represents adefect site or boundary site of the two-dimensional hydrogenboride-containing sheet, or a termination structure thereof which is notpresent in an infinitely large two-dimensional hydrogenboride-containing sheet.

INDUSTRIAL APPLICABILITY

The two-dimensional hydrogen boride-containing sheet of the presentinvention can be used as an electronic material, a catalyst carriermaterial, a superconducting material, or the like.

The invention claimed is:
 1. A two-dimensional hydrogenboride-containing sheet, comprising: a two-dimensional network thatconsists of (HB)_(n) (n≥4), wherein in an X-ray photoelectronspectroscopy, a spectrum showing a peak attributable to B1s of anegatively charged boron of approximately 187.7 eV and no peakattributable to magnesium is obtained, in an electron energy lossspectroscopy, a spectrum showing a peak attributable to sp² structure ofboron at approximately 191 eV is obtained, in a Fourier transforminfrared spectroscopy, a spectrum showing an absorption attributable toa defect site, a boundary site or a termination structure of thetwo-dimensional hydrogen boride-containing sheet at approximately 2509cm⁻¹ is obtained, and a molar ratio of boron to hydrogen determined fromthermal desorption spectroscopy and measurement of mass of thetwo-dimensional hydrogen boride-containing sheet before and afterheating the two-dimensional hydrogen boride-containing sheet is 1:1. 2.The two-dimensional hydrogen boride-containing sheet according to claim1, wherein, in the two-dimensional network, boron atoms are arranged ina hexagonal ring shape, hexagons formed of the boron atoms are connectedto one another to form a mesh-like shape, and the two-dimensionalnetwork has a site at which two adjacent boron atoms amongst the boronatoms are bound to the same hydrogen atom.
 3. The two-dimensionalhydrogen boride-containing sheet according to claim 1, wherein a lengthin at least one direction is 100 nm or longer.
 4. A production methodfor a two-dimensional boron compound-containing sheet according to claim1, the method comprising: a step of mixing, in a polar organic solvent,metal diboride having an MB₂-type structure (where M is at least oneselected from the group consisting of Al, Mg, Ta, Zr, Re, Cr, Ti, andV), with an ion exchange resin in which ions exchangeable with metalions constituting the metal diboride are coordinated.
 5. The productionmethod for a two-dimensional boron compound-containing sheet accordingto claim 4, wherein the ion exchange resin has a sulfo group.
 6. Theproduction method for a two-dimensional boron compound-containing sheetaccording to claim 4, wherein the polar organic solvent is acetonitrileor methanol.